1. Field of the Invention
The present invention relates to electrostatic copier or printer devices and particularly to a pneumatic brake for use therein.
2. Prior Art
This invention is directed to a pneumatic brake for use in connection with a data carrier, such as a paper sheet or web, where the data carrier runs over a surface of the brake element. The surface contains suction orifices through which air is sucked by a suction device.
Pneumatic brakes are conveniently employed to decelerate data carriers such as paper webs. In this, the data carrier passes over a brake surface equipped with suction orifices. Thus the data carrier can be sucked into contact with the brake surface in order to decelerate it. The surface into which the data carrier is brought into contact is herein called the brake surface. Uses of data carriers for this purpose may be found in prior art nonmechanical printers and copiers. In such constructions the data carrier may be provided with a toner image which must pass through a toner fixing station. In passing through the toner fixing station, the toner image is fused onto the data carrier.
Data fixing stations of the type used in connection with nonmechanical printers or electrostatic devices may consist of two opposed fixing cylinders, at least one of which is heated. A preheater device can be positioned upstream of the fixing cylinders in the direction of movement of the paper web. Such preheating devices may for example be a heatable saddle such as shown in U.S. Pat. No. 3,861,863.
Proper functioning of the fixing process requires that the data carrier be in intimate contact with the saddle. In order to provide the desired contact, the data carrier must be tensioned over the saddle. In order to tension the data carrier, it is known to position a pneumatic brake in front of the saddle, upstream thereof in the direction of motion of the data carrier. Downstream of the saddle a data carrier transfer device or propulsion device may be provided.
In applications of this type, the pneumatic brake has a great advantage in that the data carrier is sucked into contact with the brake surface and is thereby decelerated with the pneumatic brake engaging only the underside of the data carrier. The other side of the data carrier is then left unaffected by the brake and may therefore be used as the side on which the toner images are formed. In this manner the brake does not adversely affect such images prior to their fixing.
In order to provide uniform deceleration for data carriers of different widths, it is convenient to match the width of the brake surface containing the suction orifices to the width of the data carrier. In other words if the width of the data carrier changes, for example if it becomes smaller, then it will no longer cover all of the suction orifices in the brake surface. When this occurs the vacuum level in the pneumatic brake device decreases and the braking effect per suction orifice is lessened. It would therefore be an advance in the art to provide a pneumatic brake of the type described which reduces or eliminates the heretofore experienced loss in braking force per suction orifice occasioned by changing data carrier widths.